What are RTDs and temperature sensors?
An RTD (resistance temperature detector) is a temperature sensor whose electrical resistance changes predictably with temperature, most often using a platinum element. RTDs are the standard choice where accuracy, stability and repeatability matter. Thermocouples and thermistors cover higher-temperature and low-cost, narrow-range needs.
In most plants, a temperature sensor is a commodity. In a nuclear reactor coolant loop, an aircraft bleed-air duct or a launch vehicle propellant line, it is a qualified component whose failure has real consequences. That is where engineered sensors, documented qualification and traceable calibration earn their place.
How RTDs and other temperature sensors work
RTDs. Platinum’s resistance rises almost linearly with temperature. A Pt100 element reads 100 ohms at 0 °C and about 138.5 ohms at 100 °C. IEC 60751 defines the standard curve and tolerance classes. Elements are either wire-wound, with fine platinum wire in a ceramic or glass form, or thin-film, deposited on a substrate. Wire-wound elements remain common in demanding aerospace and nuclear designs.
Thermocouples. Two dissimilar metals joined at a measuring junction produce a small voltage that depends on the temperature difference to the reference junction. They are simple, rugged and cover very high temperatures but are less stable than RTDs.
Thermistors. Semiconductor elements change resistance sharply over a narrow range, making them sensitive and inexpensive for HVAC and equipment protection.
| Sensor | Principle | Strength | Limitation |
|---|---|---|---|
| Platinum RTD | Resistance rises with temperature | Accuracy, stability, interchangeability | Slower in heavy wells, moderate upper limit |
| Nickel RTD | Resistance rises with temperature | High sensitivity, aerospace heritage | Narrower range than platinum |
| Thermocouple | Seebeck voltage between dissimilar metals | High temperature, rugged, fast in small sizes | Lower accuracy, drift, cold junction required |
| Thermistor | Semiconductor resistance change | Very sensitive, low cost | Narrow range, nonlinear |
Nuclear qualification. A safety-related sensor must be proven to work after thermal and radiation aging and during design-basis accidents, which is the scope of IEEE 323, and through seismic shaking under IEEE 344. Qualification is tied to the exact design, materials and installation, which is why form-fit replacements for obsolete instruments are valuable to operating plants.
Common applications
- Commercial nuclear power: reactor coolant loop, pressurizer, feedwater, containment and emergency diesel generator temperatures across the Southeast’s large nuclear fleet, plus advanced reactor and small modular reactor programs.
- Aerospace and space: engine, fuel, hydraulic and environmental control sensors for aircraft, and cryogenic sensors for launch vehicles, relevant to Huntsville and the Space Coast.
- Oil, gas and petrochemical: process and equipment temperatures in Gulf Coast plants.
- Industrial and data centers: metals, HVAC and critical cooling systems.
Choosing the right temperature sensor
Accuracy on paper means little if the sensor sees the wrong temperature. Immersion depth, thermowell design, response time and wiring determine real measurement quality. Start with range and required accuracy, then define the installation and electrical connection. For regulated service, bring qualification and documentation requirements into the specification from the beginning; retrofitting them later is slow and expensive.
Manufacturers we represent for temperature sensing
Curtiss-Wright Round Rock in Round Rock, Texas, was founded as Weed Instrument in 1968, became Ultra Electronics NSPI in 2008 and joined Curtiss-Wright’s Nuclear Division at the end of 2024. The company says its temperature sensors are used for reactor coolant monitoring in more than 80% of US reactors. It builds nuclear-qualified RTDs, thermocouples and transmitters, aerospace RTDs under AS9100D, industrial sensors, and nuclear-qualified fiber-optic converters that isolate safety and non-safety signals. It also runs an A2LA-accredited ISO/IEC 17025 calibration lab.
Get local application support
Vaughn Associates helps nuclear, aerospace and industrial engineers identify replacement sensors, compare qualification options and coordinate quotes with Curtiss-Wright. Visit engineering support, request a quote, or find your area manager on the territories page.
